From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx0a-001b2d01.pphosted.com (mx0b-001b2d01.pphosted.com [148.163.158.5]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 3t7x8M5dvxzDvQr for ; Wed, 2 Nov 2016 16:13:39 +1100 (AEDT) Received: from pps.filterd (m0098419.ppops.net [127.0.0.1]) by mx0b-001b2d01.pphosted.com (8.16.0.17/8.16.0.17) with SMTP id uA25DQlJ143794 for ; Wed, 2 Nov 2016 01:13:37 -0400 Received: from e23smtp02.au.ibm.com (e23smtp02.au.ibm.com [202.81.31.144]) by mx0b-001b2d01.pphosted.com with ESMTP id 26f740kkfn-1 (version=TLSv1.2 cipher=AES256-SHA bits=256 verify=NOT) for ; Wed, 02 Nov 2016 01:13:37 -0400 Received: from localhost by e23smtp02.au.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Wed, 2 Nov 2016 15:13:34 +1000 Received: from d23relay06.au.ibm.com (d23relay06.au.ibm.com [9.185.63.219]) by d23dlp02.au.ibm.com (Postfix) with ESMTP id 399882BB0054 for ; Wed, 2 Nov 2016 16:13:32 +1100 (EST) Received: from d23av02.au.ibm.com (d23av02.au.ibm.com [9.190.235.138]) by d23relay06.au.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id uA25DWfI17563676 for ; Wed, 2 Nov 2016 16:13:32 +1100 Received: from d23av02.au.ibm.com (localhost [127.0.0.1]) by d23av02.au.ibm.com (8.14.4/8.14.4/NCO v10.0 AVout) with ESMTP id uA25DUWx007248 for ; Wed, 2 Nov 2016 16:13:32 +1100 From: Pan Xinhui To: linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, virtualization@lists.linux-foundation.org, linux-s390@vger.kernel.org, xen-devel-request@lists.xenproject.org, kvm@vger.kernel.org, xen-devel@lists.xenproject.org, x86@kernel.org Cc: benh@kernel.crashing.org, paulus@samba.org, mpe@ellerman.id.au, mingo@redhat.com, peterz@infradead.org, paulmck@linux.vnet.ibm.com, will.deacon@arm.com, kernellwp@gmail.com, jgross@suse.com, pbonzini@redhat.com, bsingharora@gmail.com, boqun.feng@gmail.com, borntraeger@de.ibm.com, rkrcmar@redhat.com, David.Laight@ACULAB.COM, dave@stgolabs.net, konrad.wilk@oracle.com, Pan Xinhui Subject: [PATCH v7 02/11] locking/osq: Drop the overload of osq_lock() Date: Wed, 2 Nov 2016 05:08:29 -0400 In-Reply-To: <1478077718-37424-1-git-send-email-xinhui.pan@linux.vnet.ibm.com> References: <1478077718-37424-1-git-send-email-xinhui.pan@linux.vnet.ibm.com> Message-Id: <1478077718-37424-3-git-send-email-xinhui.pan@linux.vnet.ibm.com> List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , An over-committed guest with more vCPUs than pCPUs has a heavy overload in osq_lock(). This is because vCPU A hold the osq lock and yield out, vCPU B wait per_cpu node->locked to be set. IOW, vCPU B wait vCPU A to run and unlock the osq lock. Kernel has an interface bool vcpu_is_preempted(int cpu) to detect if a vCPU is currently running or not. So break the spin loops on true condition. test case: perf record -a perf bench sched messaging -g 400 -p && perf report before patch: 18.09% sched-messaging [kernel.vmlinux] [k] osq_lock 12.28% sched-messaging [kernel.vmlinux] [k] rwsem_spin_on_owner 5.27% sched-messaging [kernel.vmlinux] [k] mutex_unlock 3.89% sched-messaging [kernel.vmlinux] [k] wait_consider_task 3.64% sched-messaging [kernel.vmlinux] [k] _raw_write_lock_irq 3.41% sched-messaging [kernel.vmlinux] [k] mutex_spin_on_owner.is 2.49% sched-messaging [kernel.vmlinux] [k] system_call after patch: 20.68% sched-messaging [kernel.vmlinux] [k] mutex_spin_on_owner 8.45% sched-messaging [kernel.vmlinux] [k] mutex_unlock 4.12% sched-messaging [kernel.vmlinux] [k] system_call 3.01% sched-messaging [kernel.vmlinux] [k] system_call_common 2.83% sched-messaging [kernel.vmlinux] [k] copypage_power7 2.64% sched-messaging [kernel.vmlinux] [k] rwsem_spin_on_owner 2.00% sched-messaging [kernel.vmlinux] [k] osq_lock Suggested-by: Boqun Feng Signed-off-by: Pan Xinhui Acked-by: Christian Borntraeger Acked-by: Paolo Bonzini Tested-by: Juergen Gross --- kernel/locking/osq_lock.c | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-) diff --git a/kernel/locking/osq_lock.c b/kernel/locking/osq_lock.c index 05a3785..091f97f 100644 --- a/kernel/locking/osq_lock.c +++ b/kernel/locking/osq_lock.c @@ -21,6 +21,11 @@ static inline int encode_cpu(int cpu_nr) return cpu_nr + 1; } +static inline int node_cpu(struct optimistic_spin_node *node) +{ + return node->cpu - 1; +} + static inline struct optimistic_spin_node *decode_cpu(int encoded_cpu_val) { int cpu_nr = encoded_cpu_val - 1; @@ -118,8 +123,9 @@ bool osq_lock(struct optimistic_spin_queue *lock) while (!READ_ONCE(node->locked)) { /* * If we need to reschedule bail... so we can block. + * Use vcpu_is_preempted to detect lock holder preemption issue. */ - if (need_resched()) + if (need_resched() || vcpu_is_preempted(node_cpu(node->prev))) goto unqueue; cpu_relax_lowlatency(); -- 2.4.11